The basis for the reduced proliferative response in aged T cells is unknown. This study aims to uncover aging mechanisms by: (1) determining the basis for the suppressed interleukin-2 (IL-2) synthesis in aged T cells and T cell subsets; and (2) elucidating aging defects in T cells subsets CD4 and CD8 from Hispanic and rhesus monkey donors with respect to mitogenesis, IL-2 synthesis, and growth in culture. One hallmark of the aged T cell is a decreased synthesis of IL-2. N-Acetylcysteine (NAC) enhanced mitogenesis and IL-2 secretion by 3-5 fold in our preliminary studies with aging T cells. This finding, together with other data, suggests that control of the IL-2 gene, a crucial element in the autocrine mechanism of T cell mitogenesis, may be a major target of aging mechanisms. This study will clarify the role of transcriptional regulation of IL-2 mRNA by study of the enhancement factors (EF) which regulate the IL-2 gene promotor. Our experimental design is based on quantitation of each of the six EF, which modulate the IL-2 gene, by use of oligonucleotide DNA probes. The nuclei from human and rhesus T cells and subsets, activated by ConA, anti-CD3, and anti-CD2, will be extracted and amount of each EF-probe complex determined (after electrophoresis) with the enhanced chemiluminescent technique. Should any of the EF prove depressed in aged cells, it could account for the suppressed IL-2 synthesis. Current views suggests that all six EF are required in concert to give maximal IL-2 synthesis. The effect of NAC and ascorbate, which enhance and inhibit T cell functions respectively, on EF activities will also be measured. To achieve our second objective, T cell subsets (CD4 and CD8) will be purified from rhesus and human PBMC and compared for mitogenic responses (using BrdU to avoid radiotoxicity), IL-2 synthesis using ELISA, and growth in culture. We will thereby fill a crucial gap in our understanding of T cell aging by testing the exclusivity of CD8 subset aging, as suggested by recent studies on human T cell subsets. Conclusions from most aging studies are based on responses of the whole T cell fraction, and may have to be re-interpreted. If the CD8 aging hypothesis proves correct, then mouse T cells, which age differently, would be an inappropriate model for human T cell aging. Overall, this study will advance our understanding of IL-2 gene control in aged T cells, and delineate the vulnerability of the CD4 and CD8 subsets to aging defects. NAC inhibits replication of HIV via the NF-kappa B, and is under consideration for clinical use in AIDS. Since many aged people are also immunosuppressed, our study of NAC assumes further clinical relevance.